DNA biosensors have provided a method of extracting necessary information from target genes in a quick and simple manner. For example, various DNA probes that give signals in a sequence-specific fashion, as represented by molecular beacons, have been widely used (see Non-patent Document 1 to 3). However, there are very few DNA probes that can release useful functional molecules (see Non-patent Document 4 to 6).
In a conventional method as a means of releasing a drug from a nucleic acid, photodecomposition of a nitrobenzyl group or a phenacyl group has been utilized. However, molecular design for using a method of introducing a functional molecule by a post-synthesis method is not easy, and a reaction species such as a nitroso group which is harmful to nucleic acid is generated upon release of a drug.
Furthermore, no techniques of removing a fluorescent moiety from fluorescence-modified nucleic acid have been reported.    Non-patent Document 1: Tyagi, S., et al., Nat. Biotechnol., 1996, 14, 303-308    Non-patent Document 2: Tyagi, S., et al., Nat. Biotechnol., 1998, 16, 49-53    Non-patent Document 3: Piatek, A. S., et al., Nat. Biotechnol., 1998,16, 359-363    Non-patent Document 4 Ma, Z., et al., Proc. Natl. Acad. Sci. USA, 2000, 97, 11159-11163    Non-patent Document 5: Ma, Z., et al., Med. Chem., 2001, 9, 2501-2510    Non-patent Document 6: Okamoto, A., et al., Angew. Chem. Int. Ed., 2003, 42, 2502-2504